1. Field of the Invention.
This invention pertains to safety apparatus, and more particularly to safety devices for stopping a moving storage carriage.
2. Description of the Prior Art.
Mobile storage systems for storing books and related items in libraries and offices are well known. Typically, the system includes several bookcase-like carriages which roll along rails embedded in the building floor. To securely lock a mobile carriage in place and thus prevent accidental start up and possible injury to a person in its path, various locking devices have been developed. For example, U.S. patent application Ser. No. 575,216 illustrates a rack and a spring loaded locking bar. U.S. Pat. No. 4,523,794 discloses a reciprocatable pin type locking device. However, the devices of the two mentioned patent applications are intended for locking a stationary carriage at a selected location along the system rails; they are not designed to stop a moving carriage.
Especially with storage systems which are electrically powered, it is very important that means for quickly stopping a moving carriage be available. For that purpose, it is known to install safety switches at locations easily reached by a person standing in the path of a carriage which is started by another person. Prior switches acted to break the electrical circuit to the drive motors. However, the substantial inertia of a heavily loaded carriage permitted it to coast a relatively great distance, so that a person in its path was still subject to possible injury. Further, prior switching circuits for interrupting the drive motors were of the momentary interrupt type. That is, after de-energization, the drive motors could be immediately re-energized to provide power for moving the carriage. Thus, a de-energized carriage could be restarted before a trapped person left the danger area.